The present invention relates to the formation of a silicon carbide film, particularly to beta-silicon carbide films, and more particularly to a method of fabricating polycrystalline .beta.-silicon carbide films as a protective and anti-reflective coating on a solar cell.
Silicon carbide is an attractive material for numerous applications and can exist in over 170 polytypes, most of which are hexagonal or rhombohedral .alpha.--SiC, and .alpha.--SiC and coatings thereof have been produced by various techniques and for various applications.
While SiC can exist in numerous polytypes, only one type of cubic polytype, or cubic SiC has been identified, and denoted as 3C- or .beta.--SiC. Thin films of beta silicon carbide (.beta.--SiC) are of great interest since the electron transport properties are much better than .alpha.--SiC over a wide temperature range of 27.degree.-730.degree. C. Epitaxial films of .beta.--SiC have been primarily grown by chemical vapor deposition, and chemical vapor deposition of high purity .beta.--SiC on the surface of a substrate is exemplified by U.S. Pat. No. 5,106,687 issued Apr. 21, 1992 to K. Tanino et al. By way of example, heterojunction bipolar transistor (HBT) devices have been fabricated using epitaxial .beta.--SiC emitters on Si substrates, and high DC HFE gain of 800 was observed with undetectable recombination current; see T. Sugii et al., IEEE Elec. Dev Lett 9(2) 87 (1988).
More recently, it has been found that pulsed laser processing of thin films of amorphous silicon and carbon co-deposited on various substrates produces .beta.--SiC, with very small crystallites, tens of angstroms in size, and tests have established that no other phases (Si, C, or SiC) were found. This recently found process for producing .beta.--SiC basically involves co-depositing amorphous silicon and carbon on a substrate and then irradiating the thus formed film with a pulsed energy source (e.g. an excimer laser), and is described and claimed in copending U.S. application Ser. No. 08/043,820, filed Apr. 7, 1983, entitled "Pulsed Energy Synthesis And Doping Of Silicon Carbide", and assigned to the same assignee.
A need exists in the field of solar cells for a protective coating to prevent damage to the cell and thus extend the effective life of solar cells. It has been determined that beta silicon carbide films have an extremely hard surface, and it has been recognized that such .beta.--SiC films can produce an antireflective/protective coating on a solar cell, or other applications requiring an extremely hard surface. By forming a .beta.--SiC film on a solar cell, such would prevent damage of the cell due to scratching the surface thereof during cleaning to remove accumulated debris thereon, whereby the solar cell power output can be maintained, as well as providing moisture protection without increasing the mass of the solar cell. Thus, the present invention can significantly increase the life of a solar cell, for example, as well as provide a smooth, hard surface for various applications.